linux-kernel - Re: [RFC PATCH net v2 0/3] Fix OdroidC2 Gigabit Tx link issue

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Date:   Thu, 24 Nov 2016 18:10:39 +0100
From:   Martin Blumenstingl <martin.blumenstingl@...glemail.com>
To:     Jerome Brunet <jbrunet@...libre.com>
Cc:     netdev@...r.kernel.org, devicetree@...r.kernel.org,
        Florian Fainelli <f.fainelli@...il.com>,
        Carlo Caione <carlo@...one.org>,
        Kevin Hilman <khilman@...libre.com>,
        Giuseppe Cavallaro <peppe.cavallaro@...com>,
        Alexandre TORGUE <alexandre.torgue@...com>,
        Andre Roth <neolynx@...il.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        linux-amlogic@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH net v2 0/3] Fix OdroidC2 Gigabit Tx link issue

On Thu, Nov 24, 2016 at 5:01 PM, Jerome Brunet <jbrunet@...libre.com> wrote:
> On Thu, 2016-11-24 at 15:40 +0100, Martin Blumenstingl wrote:
>> Hi Jerome,
>>
>> On Mon, Nov 21, 2016 at 4:35 PM, Jerome Brunet <jbrunet@...libre.com>
>> wrote:
>> >
>> > This patchset fixes an issue with the OdroidC2 board (DWMAC +
>> > RTL8211F).
>> > Initially reported as a low Tx throughput issue at gigabit speed,
>> > the
>> > platform enters LPI too often. This eventually break the link (both
>> > Tx
>> > and Rx), and require to bring the interface down and up again to
>> > get the
>> > Rx path working again.
>> >
>> > The root cause of this issue is not fully understood yet but
>> > disabling EEE
>> > advertisement on the PHY prevent this feature to be negotiated.
>> > With this change, the link is stable and reliable, with the
>> > expected
>> > throughput performance.
>> I have just sent a series which allows configuring the TX delay on
>> the
>> MAC (dwmac-meson8b glue) side: [0]
>> Disabling the TX delay generated by the MAC fixes TX throughput for
>> me, even when leaving EEE enabled in the RTL8211F PHY driver!
>>
>> Unfortunately the RTL8211F PHY is a black-box for the community
>> because there is no public datasheeet available.
>> *maybe* (pure speculation!) they're enabling the TX delay based on
>> some internal magic only when EEE is enabled.
>
> Hi already tried acting on the register setting the TX_delay. I also
> tried on the PHY. I never been able to improve situation on the
> Odroic2. Only disabling EEE improved the situation.
OK, thanks for clarifying this!

> To make sure, i tried again with your patch but the result remains
> unchanged. With Tx_delay disabled (either the mac or the phy), the
> situation is even worse, it seems that nothing gets through
This is interesting, because in your case you should have a 4ns TX
delay (2ns from the MAC and presumably 2ns from the PHY).
Maybe that is also the reason why the TX delay is configurable in 2ns
steps in PRG_ETHERNET0 on Amlogic SoCs.

out of curiosity: have you tried setting a 4ns (half clock-cycle) TX
delay for the MAC and disabling it in the PHY?


Regards,
Martin